Volume Oscillations Research Articles

Mechanism of Chip Segmentation in Orthogonal Cutting of Zr-Based Bulk Metallic Glass

Abstract Bulk metallic glasses (BMGs) are a series of metal alloys with an amorphous structure. The deformation of BMGs occurs in localized regions and is highly sensitive to the applied stress, strain rate, and temperature. This paper presents a coupled thermomechanical model to analyze the chip segmentation mechanism due to material shear localization in orthogonal cutting of Zr-BMG. The shear stress variation in the primary shear zone is modeled considering the tool-chip friction and large strain of the material. The constitutive property of BMG corresponding to the inhomogeneous deformation through shear transformation zones is modeled. The oscillations of shear stress, temperature, and free volume are simulated based on the cutting conditions. The predicted chip segmentation frequency is compared with the experimental result under different cutting speeds and uncut chip thicknesses. The developed model provides the fundamental mechanism of material deformation and chip formation in cutting Zr-BMG with an amorphous structure.

Heat Transfer Performance of a Gasketed Plate Heat Exchanger using Nanofluid and Subject to Vibration as a Combined Augmentation Techniques

In the present study, an experimental investigation for heat transfer performance of γAl2O3-water nanofluid through a gasketed plate heat exchanger (GPHE) subjected to a low amplitude mechanical vibration was studied. γAl2O3-water nanofluid with four different volume fractions have been prepared and used as the hot working fluid. Corrugated plate heat exchanger (PHE) with six stainless steel plates; creating three cold municipal water channels and two hot nanofluid channels in counter flow pattern. GPHE is subjected to vibration by means of a grinding motor. Vibration frequencies is varied from 13.33 to 46.67 cps and vibrational dimensionless amplitude (A/De) is varied from 9.14x10-3 to 52.66x10-3. The experiments have been conducted in the Reynolds number ranging from 730 to 3400. The results revealed that as vibrational dimensionless amplitude (A/De) and nanofluid volume fractions increases the net heat transfer coefficient enhancement ratio increases. The net heat transfer coefficient increases as mechanical vibration amplitude decreases. The maximum net heat transfer coefficient enhancement ratio is 64%, which is achieved at 0.51 % volume fraction and oscillation Reynolds number of 211.34, which was occur just after the resonance condition. Moreover, a new empirical correlation is proposed to predict the GPHE Nusselt number Finally, pressure drop is measured and found that it is increased as nanofluid volume fraction increased.

Numerical unsteady simulation of nanofluid flow over a heated angular oscillating circular cylinder

In this study, laminar unsteady two-dimensional incompressible nanofluid flow is numerically investigated over a heated circular cylinder under angular oscillations about its own axis. Governing equations include Navier–Stokes, and energy equations have been solved numerically using finite volume method. Simulations were carried out in $$100 \le Re \le 200$$, $$0.5 \le F \le 2$$ and $$\varTheta_{\text{A}} = {\raise0.7ex\hbox{$\pi $} \!\mathord{\left/ {\vphantom {\pi 4}}\right.\kern-0pt} \!\lower0.7ex\hbox{$4$}} , {\raise0.7ex\hbox{$\pi $} \!\mathord{\left/ {\vphantom {\pi 2}}\right.\kern-0pt} \!\lower0.7ex\hbox{$2$}}$$. Also CuO–water nanofluid was utilized in various volume fractions of $$0 \le \varphi \le 3\%$$ range. Thermophysical properties of nanofluid were assumed to be temperature dependent. Lock-on phenomenon has been detected and its effects on the fluid flow, and heat transfer characteristics have been illustrated. The effects of solid particles volume fraction and oscillation parameters on the vortex shedding, mean velocity contours, mean drag and lift coefficients, temperature field, heat transfer coefficient and power spectral density diagrams have been investigated in detail. Obtained results indicate that utilization of nanofluids is more preferable, since oscillating the cylinder leads to dissipation in engineering equipments which would deduce the efficiency compared to using nanofluids.

Potential energy states and mechanical properties of thermally cycled binary glasses

Abstract

Carbon dioxide diffusion coefficient in noninvasive high-frequency oscillatory ventilation.

The carbon dioxide (CO2 ) diffusion coefficient (DCO 2 ) reflects CO 2 removal during high-frequency oscillatory ventilation (HFOV). We hypothesized that despite leak flow during noninvasive HFOV (nHFOV) DCO 2 continues to indicate ventilation efficacy. A neonatal airway model including CO2 production and an adjustable oropharyngeal leak was connected to a ventilator via bi-nasal prongs. Pressures and gas flows were measured at prongs, trachea, and leak. Oscillatory tidal volumes below (V T trachea ) and above the leak (V T prong ) were calculated from tracheal and leak flows. DCO 2 was calculated using V T trachea (DCO 2 trachea ) and V T prong (DCO 2 prong ) and compared with CO 2 partial pressure (pCO 2 ). Effects of leak flow (0, 5, or 10L/min) on DCO 2 were assessed at fixed pressure amplitudes or predefined oscillatory volumes under steady-state pCO 2 conditions in the modeled lung. DCO2 trachea correlated strongly with pCO 2 , independent of the leak flow level (P < 0.0001). DCO 2 prong correlated with pCO 2 without and with moderate leak (P < 0.0001) but not with maximum leak (P = 0.1432). V T trachea correlated with the quotient of tracheal pressure amplitude and frequency irrespective of the leak (P < 0.0001). Based on the pressure amplitude at prong level (A prong ) V T trachea continued to follow a linear model of which the slopes decreased with increasing leak flow. V T prong correlated with the quotient of A prong and frequency, irrespective of the leak (P < 0.0001). DCO2 obtained at the airway opening at prong level reflects ventilation efficacy during nHFOV even in the presence of moderate oropharyngeal leak.

Influence of the Local Field and Dipole-Dipole Interactions on the Spectral Characteristics of Simple Metals and Their Nanoparticles

The effect of dipole-dipole interactions of free electrons on the spectral characteristics of simple metals and their nanoparticles is analyzed using Drude theory and the model of the Lorentz local field. It is established that accounting for the dispersion of a local field under conditions of one-dimensional (1D) confinement based on the optical constants of the bulk metal allows the determination of its spectral micro-characteristics in the frequency region of the longitudinal collective motions of the free electrons. This corresponds to the spectra of the dielectric losses of bulk plasma oscillations. A similar procedure for three-dimensional (3D) confinement produces the spectrum of dielectric losses at the frequency of localized plasma oscillations. Using a number of simple metal examples, viz., Li, Na, and K, and also Al, Be, and Mg, it is shown that the frequencies of volume and localized plasma oscillations obtained from a model of dispersion of the local field in the long-wave limit are in good agreement with the actual frequencies of the plasma oscillations of the corresponding metals and the absorption maxima of their nanoparticles with a radius of 2–20 nm. It is shown that the frequencies of the main mode of longitudinal plasma oscillations and the absorption frequency of localized plasmons are well described using the dynamic theory of crystal lattice vibrations.

Analysis of backflow effect in a centrifugal pump

Backflow might appear near the impeller inlet under low discharge conditions due to excessive pressure difference near the blade leading edge. The shear layer between the swirling backflow and the main flow rolls up and forms a backflow vortex at the impeller’s inlet. Backflow vortex cavitation occurs at the vortex core if the pressure there drops lower than vapor pressure. In order to investigate the effect of backflow on pressure, flow rate and cavity volume, the backflow phenomena for a centrifugal pump was calculated using SST k-omega turbulence model and Rayleigh-Plesset cavitation model. Results show that the general flow characteristics are correctly predicted. Furthermore, the development of cavities and backflow have been illustrated in this paper. It is also shown that the backflow occurring at the inlet of impeller significantly affects the general performance of the centrifugal pump. The generation and collapse of the cavities caused by the backflow lead to the oscillation of cavity volume, which is the main reason for large-cycle fluctuation of inlet flow rate.

Frequency-resolved analysis of coherent oscillations of local cerebral blood volume, measured with near-infrared spectroscopy, and systemic arterial pressure in healthy human subjects.

We report a study on twenty-two healthy human subjects of the dynamic relationship between cerebral hemoglobin concentration ([HbT]), measured with near-infrared spectroscopy (NIRS) in the prefrontal cortex, and systemic arterial blood pressure (ABP), measured with finger plethysmography. [HbT] is a measure of local cerebral blood volume (CBV). We induced hemodynamic oscillations at discrete frequencies in the range 0.04–0.20 Hz with cyclic inflation and deflation of pneumatic cuffs wrapped around the subject’s thighs. We modeled the transfer function of ABP and [HbT] in terms of effective arterial (K(a)) and venous (K(v)) compliances, and a cerebral autoregulation time constant (τ(AR)). The mean values (± standard errors) of these parameters across the twenty-two subjects were K(a) = 0.01 ± 0.01 μM/mmHg, K(v) = 0.09 ± 0.05 μM/mmHg, and τ(AR) = 2.2 ± 1.3 s. Spatially resolved measurements in a subset of eight subjects reveal a spatial variability of these parameters that may exceed the inter-subject variability at a set location. This study sheds some light onto the role that ABP and cerebral blood flow (CBF) play in the dynamics of [HbT] measured with NIRS, and paves the way for new non-invasive optical studies of cerebral blood flow and cerebral autoregulation.

Volume oscillation and acoustical scattering of a gas bubble

The exact solution of a gas bubble’ volume was obtained based on volume oscillation of a gas bubble. The volume pulsation, acoustic impedance, scattering pressure of a gas bubble, acoustical power of scattering and acoustical scattering cross section of a single bubble are researched in a small amplitude acoustic field. The results show that a big bubble oscillates more violently than that of a small bubble in a weak acoustic field if the linear resonance does not happen. The occurrence of a linear resonance response of a single bubble leads to the volume oscillation and the scattering ability of a gas bubble become stronger. Additionally, the scattering cross section does not depend on the driving pressure. The amplitude of scattering pressure of a big bubble can reach the magnitude compared to the driving pressure when the resonance response occurs.

ХВИЛЬОВА СТРУКТУРА ГЕМОДИНАМІЧНИХ ПОКАЗНИКІВ В ОСІБ ІЗ РІЗНИМ ВИХІДНИМ РІВНЕМ СЕРЦЕВОГО ВИКИДУ ТА КРОВОНАПОВНЕННЯ ОРГАНІВ ГРУДНОЇ КЛІТКИ

Introduction . Wave fe atures of the duration of cardiointervals (t-R-R) and s troke volume of blood are considered as a reflection of the dynamics of regulatory processes in the body. Significant differences in healthy young men in values of cardiac index and blood supply of the thoracic organs condition on the peculiarities of regulation of the cardiovascular system. Purpose . To find out the peculiarities of the wave structure of oscillations (t-R-R) and s troke volume of blood (SV) in individuals with different baseline cardiac output and blood supply. Methods . The resulting time series were analyzed by 5-min implementations of secuential SV and t-R-R in «Caspico» program . For the duration of the cardiointervals, three main spectral components were distinguished: HF (0.15-0.4 Hz), LF (0.04-0.15 Hz), VLF (0-0.04 Hz), and total spectrum power (TP), the power of high-frequency oscillations in normalized units (HFnorm). For SV, such indicators were HF sv , LF sv , VLF sv , TP sv and HF norm SV , respectively. Results . At rest, the highest t- R - R oscillation power in the LF and HF ranges was established in hypokinetics, the SV oscillation power in the 0.04-0.15 Hz frequency band was significantly higher in hyperkinetics compared to eukinetics, in HF norm SV - it was probably higher in hyperkinetics than hypokinetics. When functional tests were performed, the greatest differences between groups of individuals with different typology by cardiac output were observed at dosed physical activity: HFnorm in hypokinetics was authentically smaller than in the representatives of other groups, LF was larger than in eukinetics, and HF was lower than in hyperkinetics. The initial level of blood supply of the thorax also authentically influenced the peculiarities of oscillations of the hemodynamic indicators of healthy young men under different conditions. At rest in the supine position, individuals with low levels of blood supply of thoracic organs had authentically a higher power of high-frequency oscillations t-R-R than men with an average value of this index, and relatively larger intergroup differences were observed in the parameters of SV oscillations. According to the indicators of the wave structure of t-R-R and SV with active orthopedic testing and with mental load, the lowest activation of the sympathetic nervous system was observed in the group of men with low initial level of blood supply of the thoracic organs. . Originality . The peculiarities of the regulatory rhythms of hemodynamics are revealed in persons with different typology by the level of cardiac output and blood supply of the thoracic organs . Significant differences in the power of oscillations of cardio-interval duration and stroke volume are shown in persons of different types of hemodynamics at rest and at the dosed physical activities. Conclusions . At rest and mainly at physical activity , the features of hemodynamics oscillations have been found between persons with different initial levels of cardiac output, which are of compensatory nature for maintaining cardiac output for hypokinetics, and are caused by different levels of blood supply in the thoracic organs. The wave structure of the regulatory rhythms of hemodynamics and its changes at loads significantly depend on the initial level of blood supply of the thorax , which is shown by the relatively less tension of the mechanisms of regulation in persons of the extreme groups. Taking into account individual-typological characteristics of a person can increase the diagnostic value of methods of analysis and evaluation of the wave structure of hemodynamic parameters, as well as identify new directions in preventive medicine and health insurance.

Effect of high frequency oscillatory high flow nasal cannula on carbon dioxide clearance in a premature infant lung model: A bench study.

This study compared CO2 clearance in a premature infant lung model connected to a high flow nasal cannula (HFNC) system supplied with oscillatory versus non-oscillatory flow. The lung model was set to compliance 1.0 mL/cmH2 O, RR 60 breaths/min, and 6 mL tidal volume. A 100% CO2 was injected at a constant 15 mL/min. To create oscillation, HFNC flow was interrupted at rates of 4-6-8 and 10 Hz. equilibrated end-tidal CO2 (ETCO2 ) was recorded with and without oscillation at set flows of 2-8 L/min and repeated for each oscillation frequency. Overall ETCO2 decreased significantly (P < 0.001) during both non-oscillatory and oscillatory HFNC as set flow increased from 2 to 8 L/min by 26.3% and 60.8%, respectively. Oscillatory ETCO2 levels decreased linearly compared to non-oscillatory HFNC with negligible difference at 2 L/min and a 48.4% difference at 8 L/min (P < 0.001). There were no differences in ETCO2 levels between oscillation frequencies at any flow except at 6 Hz for which ETCO2 was significantly lower (P < 0.01) than at 4, 8, and 10 Hz for 5-8 L/min HFNC flows. Amplitude of volume oscillations increased with increasing flow from 0.5 mL at 2 L/min to 4.0 mL at 8 L/min (P < 0.001), and decreased with increasing oscillation frequency. Oscillatory HFNC as compared to non-oscillatory was associated with significantly improved CO2 clearance in this premature infant lung model. This simple modification of the HFNC system may prove to be a useful enhancement to this mode of non-invasive respiratory support for preterm infants at high risk for respiratory failure.

Effects of Nonlinear Propagation of Focused Ultrasound on the Stable Cavitation of a Single Bubble

Many biomedical applications such as ultrasonic targeted drug delivery, gene therapy, and molecular imaging entail the problems of manipulating microbubbles by means of a high-intensity focused ultrasound (HIFU) pressure field; namely stable cavitation. In high-intensity acoustic field, bubbles demonstrate translational instability, the well-known erratic dancing motion, which is caused by shape oscillations of the bubbles that are excited by their volume oscillations. The literature of bubble dynamics in the HIFU field is mainly centered on experiments, lacking a systematic study to determine the threshold for shape oscillations and translational motion. In this work, we extend the existing multiphysics mathematical modeling platform on bubble dynamics for taking account of (1) the liquid compressibility which allows us to apply a high-intensity acoustic field; (2) the mutual interactions of volume pulsation, shape modes, and translational motion; as well as (3) the effects of nonlinearity, diffraction, and absorption of HIFU to incorporate the acoustic nonlinearity due to wave kinematics or medium—all in one model. The effects of acoustic nonlinearity on the radial pulsations, axisymmetric modes of shape oscillations, and translational motion of a bubble, subjected to resonance and off-resonance excitation and various acoustic pressure, are examined. The results reveal the importance of considering all the involved harmonics and wave distortion in the bubble dynamics, to accurately predict the oscillations, translational trajectories, and the threshold for inertial (unstable) cavitation. This result is of interest for understanding the bubble dynamical behaviors observed experimentally in the HIFU field.

Determining the surface dilational rheology of surfactant and protein films with a droplet waveform generator

Understanding rheological properties of surfactant and protein films plays a crucial role in a variety of industrial and research areas, such as food processing, cosmetics, and pharmacology. To determine the surface dilational modulus using drop shape analysis, one needs to measure the dynamic surface tension in response to a sinusoidal oscillation of the surface area of the droplet. Despite many applications of drop shape analysis in studying interfacial rheology, oscillation of the droplet surface area is usually controlled in an indirect manner. Existing methods are only capable of controlling volume oscillations of the droplet rather than its surface area. We have developed an arbitrary waveform generator (AWG) to directly oscillate the surface area of a millimeter-sized droplet in a predefined sinusoidal waveform. Here, we demonstrated the capacity of this AWG, in conjunction with constrained drop surfactometry (CDS), in studying the surface dilational rheology of adsorbed surfactant and protein films. It is found that the surface dilational modulus determined for a dilute surfactant (C12DMPO) and two protein solutions (bovine serum albumin and β-casein) revealed their adsorption mechanisms. Our methods hold promise in studying the interfacial rheology of various thin-film materials, biomembranes, foams, and emulsions.

Dynamics of the Blade Channel of an Inducer Under Cavitation-Induced Instabilities

A high-head three-bladed inducer has been equipped with pressure taps on the hub along the blade channels with the aim of more closely investigating the dynamics of cavitation-induced instabilities developing in the impeller flow. Spectral analysis of the pressure signals obtained from two sets of transducers mounted both in the stationary and rotating frames has allowed to characterize the nature, intensity, and interactions of the main flow instabilities detected in the experiments: subsynchronous rotating cavitation (RC), cavitation surge (CS), and a high-order axial surge oscillation. A dynamic model of the unsteady flow in the blade channels has been developed based on experimental data and on suitable descriptions of the mean flow and the oscillations of the cavitating volume. The model has been used for estimating at the inducer operating conditions of interest the intensity of the flow oscillations associated with the occurrence of the CS mode generated by RC in the inducer inlet.

Abstract 16918: Non-Invasive Diagnosis of Pulmonary Vascular Disease Using Inhaled 129-XenonMRI

Introduction: Pulmonary arterial hypertension (PAH) carries significant morbidity and mortality. Its diagnosis requires meeting specific hemodynamic and clinical criteria and can be particularly challenging in patients with concomitant heart or lung disease. Hyperpolarized 129 Xenon ( 129 Xe) magnetic resonance imaging and dynamic spectroscopy may overcome these challenges, providing a non-invasive new tool to diagnose and monitor PAH. This is based on its unique cardiogenic oscillations reflected in the 129 Xe spectrum as it transfers to red blood cells (RBCs, Figure). Hypothesis: We hypothesized that changes in the RBC 129 Xe spectroscopic parameters will discriminate PAH from healthy volunteers, patients with left heart failure, idiopathic pulmonary fibrosis (IPF) or chronic obstructive pulmonary disease (COPD). Methods: 129 Xe spectra were dynamically acquired every 20 milliseconds in all subjects. At each time point, the amplitude, chemical shift, linewidth, and phase of the 129 Xe-RBC resonance was calculated. Cardiogenic oscillations in these spectral parameters were compared using the Kruskal-Wallis test, followed by pairwise comparisons with the Wilcoxon rank sum test. Results: A total of 14 healthy volunteers, 10 subjects with PAH, 5 subjects with left heart failure, 9 subjects with IPF, and 7 subjects with COPD underwent 129 Xe spectroscopy. In patients with PAH, RBC amplitude oscillations were significantly reduced compared to those with IPF (p &lt; 0.001) or healthy subjects (p = 0.0064, Figure). Oscillations in chemical shift and phase were only observed in IPF patients. Conclusions: 129 Xenon dynamic spectroscopy produces different RBC signatures in patients with PAH, IPF, and healthy volunteers. 129 Xe uniquely probes the alveolar-capillary interface and can thus detect the effect of arterial lesions on capillary blood volume oscillations.

Combining polymer-bound catalyst with polymeric substrate for reproducible pH oscillations in palladium-catalysed oxidative carbonylation of alkynes

Palladium-catalysed oxidative carbonylation (PCOC) of alkynes is a promising engine for building smart pulsatile polymeric systems, as it has demonstrated (in certain configurations) sustained regular oscillations in pH and redox potential for up to one month of monitoring in a batch reactor. Recent developments in polymer-supported palladium catalysts have demonstrated the full capacity of this reaction – in a macrogel that experienced oscillations in volume, while releasing a drug load. In this work, we demonstrate reproducible oscillations (more than 100 h duration) in a proline-functionalised chitosan-palladium system (Chi-Pro-Pd), using both small molecule (phenylacetylene) and polymeric (pegylated dialkyne) substrate, for the first time. Moreover, by functionalising chitosan with proline ligands, we dramatically reduced halide-mediated leaching of palladium, which readily occurred in non-functionalised chitosan-palladium catalysts (Chi-Pd). Oscillatory patterns for both systems confirm the need for fabricating functionalised chitosan supports to improve catalyst reusability and minimise loss of palladium.

Dynamic cerebral autoregulation estimates derived from near infrared spectroscopy and transcranial Doppler are similar after correction for transit time and blood flow and blood volume oscillations

We analysed mean arterial blood pressure, cerebral blood flow velocity, oxygenated haemoglobin and deoxygenated haemoglobin signals to estimate dynamic cerebral autoregulation. We compared macrovascular (mean arterial blood pressure-cerebral blood flow velocity) and microvascular (oxygenated haemoglobin-deoxygenated haemoglobin) dynamic cerebral autoregulation estimates during three different conditions: rest, mild hypocapnia and hypercapnia. Microvascular dynamic cerebral autoregulation estimates were created by introducing the constant time lag plus constant phase shift model, which enables correction for transit time, blood flow and blood volume oscillations (TT-BF/BV correction). After TT-BF/BV correction, a significant agreement between mean arterial blood pressure-cerebral blood flow velocity and oxygenated haemoglobin-deoxygenated haemoglobin phase differences in the low frequency band was found during rest (left: intraclass correlation=0.6, median phase difference 29.5° vs. 30.7°, right: intraclass correlation=0.56, median phase difference 32.6° vs. 39.8°) and mild hypocapnia (left: intraclass correlation=0.73, median phase difference 48.6° vs. 43.3°, right: intraclass correlation=0.70, median phase difference 52.1° vs. 61.8°). During hypercapnia, the mean transit time decreased and blood volume oscillations became much more prominent, except for very low frequencies. The transit time related to blood flow oscillations was remarkably stable during all conditions. We conclude that non-invasive microvascular dynamic cerebral autoregulation estimates are similar to macrovascular dynamic cerebral autoregulation estimates, after TT-BF/BV correction is applied. These findings may increase the feasibility of non-invasive continuous autoregulation monitoring and guided therapy in clinical situations.

An iPhone Application for Blood Pressure Monitoring via the Oscillometric Finger Pressing Method

We developed an iPhone X application to measure blood pressure (BP) via the “oscillometric finger pressing method”. The user presses her fingertip on both the front camera and screen to increase the external pressure of the underlying artery, while the application measures the resulting variable-amplitude blood volume oscillations via the camera and applied pressure via the strain gauge array under the screen. The application also visually guides the fingertip placement and actuation and then computes BP from the measurements just like many automatic cuff devices. We tested the application, along with a finger cuff device, against a standard cuff device. The application yielded bias and precision errors of −4.0 and 11.4 mmHg for systolic BP and −9.4 and 9.7 mmHg for diastolic BP (n = 18). These errors were near the finger cuff device errors. This proof-of-concept study surprisingly indicates that cuff-less and calibration-free BP monitoring may be feasible with many existing and forthcoming smartphones.

The Mid-Pleistocene Transition induced by delayed feedback and bistability

The Mid-Pleistocene Transition, the shift from 41 kyr to 100 kyr glacial-interglacial cycles that occurred roughly 1 Myr ago, is often considered as a change in internal climate dynamics. Here we revisit the model of Quaternary climate dynamics that was proposed by Saltzman and Maasch (1988). We show that it is quantitatively similar to a scalar equation for the ice dynamics only when combining the remaining components into a single delayed feedback term. The delay is the sum of the internal times scales of ocean transport and ice sheet dynamics, which is on the order of 10 kyr. We find that, in the absence of astronomical forcing, the delayed feedback leads to bistable behaviour, where stable large-amplitude oscillations of ice volume and an equilibrium coexist over a large range of values for the delay. We then apply astronomical forcing. We perform a systematic study to show how the system response depends on the forcing amplitude. We find that over a wide range of forcing amplitudes the forcing leads to a switch from small-scale oscillations of 41 kyr to large-amplitude oscillations of roughly 100 kyr without any change of other parameters. The transition in the forced model consistently occurs near the time of the Mid-Pleistocene Transition as observed in data records. This provides evidence that the MPT could have been primarily a forcing-induced switch between attractors of the internal dynamics. Small additional random disturbances make the forcing-induced transition near 800 kyr BP even more robust. We also find that the forced system forgets its initial history during the small-scale oscillations, in particular, nearby initial conditions converge prior to transitioning. In contrast to this, in the regime of large-amplitude oscillations, the oscillation phase is very sensitive to random perturbations, which has a strong effect on the timing of the deglaciation events.

Three-dimensional numerical investigation of a single bubble behavior against non-linear forced vibration in a microgravity environment

A single gas bubble behavior under non-linear oscillating excitation of the liquid container is studied numerically. The volume of fluid (VOF) method is used for the interface tracking between gas and liquid, implemented in the open source OpenFOAM CFD toolbox. The surface tension force at the interface is evaluated using the continuum surface force (CSF) model. Bubble behavior under forced vibration is examined by considering translational motion and shape deformation of the bubble, while the volume oscillations are ignored regarding the applied frequency range (f < 250 Hz). Bubble response to the forced vibration is studied in three types of regular oscillation, chaotic oscillation, and bubble breakup. It is shown that the inertia of the surrounding liquid and the bubble shape at the beginning of each period have the main effects on the bubble breakup. In order to survey the chaotic response, bubble shape is decomposed into a linear sum of the second to ninth shape modes using Legendre polynomials. The results obtained from the modal analysis of the bubble shape oscillation reveal that the bubble response is regular at frequencies below the second mode natural frequency of the bubble. On the other hand, bubble shape oscillation is chaotic at frequencies close to the third mode natural frequency, which in turn causes the erratic motion of the bubble in the liquid. Finally, the bubble responses to a wide range of frequencies and amplitudes are presented in a diagram based on the Bond number (the ratio of the vibration force to the surface tension force, Bo) and the ratio of the vibration amplitude to the bubble diameter (A/D).